From the past, an apparatus which is mounted on an automobile and generates output by converting a rotary motion of a motor into a linear motion by means of a ball screw has been known. For example, Japanese Patent Application Publication No. 2007-187262 describes an electric actuator which converts a rotary motion of an electric motor into a linear motion using a ball screw mechanism to drive an output shaft to perform a certain linear motion (see claim 1, and ‘Field of the disclosure’).